Process of purifying and dewaxing mineral oils



Dec. 29, 1936..

PRocEss .oF PURIFYING AND DEWAXING MINERAL oILs V Filed June 27, 1935Apo/r/a/VAL Pl/MPJ G. J. sTREzYNsKl 26,066,165

Patented Dec. 29, 1936 UNITED STATES PROCESS OF PURIFYING AND DEWAXINGMINERAL OILS George J. Strezynski, Poughkeepsie, N. Y., as-

signor to The De Laval Separator Company, New York, N. Y., a corporationof New Jersey Application June 27, 1935, Serial No. 28,656

2 Claims.

In an application led by me June 27, 1935, Serial No. 28,655, I describea process for purifying and dewaxing mineral oil containing bothamorphous and crystalline waxes and producing therefrom a dewaxedlubricating oil having a high pour test. In this process, which ispreferably applied to crude oil from which no or feW light fractionshave been distilled, but which is also applicable to any heavy fractionof the crude, such as the long residuum containing all or most of thelubricating fractions, the crude is blended with any suitable lightdiluent, such as naphtha or other light hydrocarbon, and the blend issubjected to chilling, preferably shock chilling with pronouncedagitation, to reduce its temperature to approximately 35 F. below thedesired pour point of the finished oil. The diluent is added in suchproportion that the treated blend, after addition of acid, will, whencentrifuged with a force 6000 times gravity, gives a heavy layer of waxyacid sludge not less than 15% or more than 30% of the mass of thechilled and treated blend. After the chilling step, wherein all the wax,amorphous and crystalline, is precipitated (that is, all the wax isprecipitated down to the temperature of the pour point desired), acontinuous stream of acid is added to the continuous stream of themixture of oil and wax owing from the chiller and the two streams aresubjected to a mixing action, the acid combining with undesirablecompounds (impurities) in the oil and wax to form a waxy acid sludge.The treated mixture then flows continuously to a centrifuge wherein apurified completely dewaxed oil is separated from the sludge.

In the process set forth in said application, the oil is chilled, forexample, to a temperature of approximately 16 F. if it is desired toproduce a finished lubricating oil having a pour point of 20 F., or toapproximately 35 F. if the nished lubricating oil is desired to have apour point of F. In the specific example of the process therein given,there is treated a typical east Texas paraffin base (more accuratelymixed base) crude containing gasoline about 29%, kerosene about 14%, gasoil about 21%, wax and asphaltic material about 12% (wax about 8%) andlubricating oil constituents 1'7-18%, which, when separated, give alubricating oil having a pour point of 20 F., viscosity index 86 andviscosity 67.

The present process is not concerned with the centrifugal separatingstep of the process whereby there is secured a maximum yield of thequality of oil desired, but relates to the acid. addition step of theprocess and particularly to the temperature of the acid added in itsrelation to the temperature to which the oil ischilled. The temperatureof chilling, dependent Aon the desired pour point of the finished oil,may vary from about 0 F. to 50 F. Since the freezing point of sulfuricacid of the high concentrations that give the best results may vary fromabout 8 F.

to not much above 30 F. (usually in the upper mixture of cold oil andwax. 'Ihe reaction con- Y sequently proceeds so slowly that eventually acertain amount of acid freezes into hard crystals and causes cloggingand overflow. The use of fuming acid has been suggested, but thefreezing point of fuming acid is higher than that of 98% acid.

I have found, however, that if the oil is chilled to a temperature morethan 30% below that of the desired pour point of the finished oil, thatis, below what has been deemed necessary, and if the added acid is at asubstantially higher temperature than that hitherto employed, thechemical reaction is so far expedited and the heat generation so faraccelerated that the reaction will be completed before the acid issufciently reduced in temperature to freeze, thereby eliminating theclogging elfect of acid crystals. While the temperature of the oil andWax mixture is thereby raised more than it otherwise would be, it Willnot be raised above the permissible maximum if, in the initial chilling,it is chilled to only a very few degrees below the temperature requiredif the acid were added while comparatively cold. To prevent freezing,the temperature of the acid sho-uld be above 110 F. More desirably itshould be added at a temperature within about F. of 150 F. It will beunderstood that the hotter the acid, the greater must be the degree ofrefrigeration. It is permissive to add the acid at a temperaturesubstantially higher than 150 F., but it is uneconomical to do do so,since it involves the expense of refrigeration to a lower temperaturewith no corresponding gain.

The amount of acid added may be varied Within limits at the discretionof the operator. The

desirable amount will vary with the desired pour test of the finishedoil. Thus, in producing 20 F. pour test oil, a preferable addition ofacid is about 12 to 14 pounds per barrel of oil, or about 21/2%; Whilein producing 0 F. pour test oil, a preferable addition of acid is about24 to 28 pounds, or about 5%. The amount of acid in these examples isabout 20% moreL than is used in conventional methods and is distinctlyabove the amount required to produce the necessary reaction. Theaddition of acid in such substan- 5 tial excess is of advantageinvseveral respects. It insures a sufficient gravity differentialbetween the oil and sludge. It speeds the reaction. It results in theproduction of a lubricat-` ing oil having a higher viscosity indexnumber than is obtainable by the addition of a smaller quantity. Itdecreases the temperature spread between the operation temperature andthe pour point of the finished oil. I Referringto the drawing, which isa diagram or flow sheet of an apparatus for practicing the abovedescribed process: Separate streams of the oil tor be dewaxed andpurifiedV (which may be crude oilV of the character hereinbeforedescribed) Yand a diluent, such as naphtha, are delivered'to a blendingtank I0, whence the oil is pumped through a chiller II and thereinsub-cooled to a temperature. of about l35 `F. below the desired pourtest of the finished oil. The chilling operation will precipitate allthe wax which precipipitates at the temperature of chilling. By means ofa pump I2 the mixture of oil and wax is conveyed to a mixer I4, whichmay be a centrifugal pump. YInto the oil line leading to the mixer I4 isconveyed, through a pump I3, a stream of concentrated sulfuric acid(preferably about 98% H2804) at a temperature of about 150 F. The mixingmay be completed in the pump I4, or it may berun through an additionalmixer I5, which maybe a series of centrifugal pumps. The acid reactswith the oil and forms a mixture of waxy acid sludge and oil, the latterusually containing'wax in ne suspension but otherwise purified. Themixture is then conveyed to a centrifuge I6, which is specially designedto act upon the mixture so as to enable the recovery of completelydewaxed oil. Suitable centrifuges are shown in patents granted to meDecember 3, 1935, No. 2,022,814, No. 2,022,815, No. 2,022,816, and No.2,022,817.

It will be understood that I do not herein claim, separate and apartfrom the above described process, certain novel features thereof, suchas the regulation of the percentage of the diluent, which form thesubject matter of an application filed by Strezynski and Pfau July25,1935, Serial No. 33,073. n n

What I claim and desire to protect by Letters Patent is:

1. In the process of purifying and dewaxing mineral oil to obtaintherefrom high test pour oil, which comprises chilling the oil to atemperature below 0 F. to precipitate the wax, mixing concentratedsulfuric acid with the mixture of oil and precipitated wax andcentrifuging the resultant mixture of waxy acid sludge and purifieddewaxed oil and thereby effecting their separation; the improvementwhich comprises,in the chilling operation, sub-cooling the oil below thetemperature that would be required, if cold acid were added, tosubsequently produce purified dewaxed oil of the desired pour point,and, in the acid treating operation, adding the acid While at atemperature above F. to thereby, by accelerating the generation of heatby the reaction, prevent freezing of the acid before completion of theraction.

2. In the process of purifying and dewaxing mineral oil to obtaintherefrom high testV pour oil, whichfcomprises chilling the oil to atemperature below 0 F. to precipitate the wax, mixing concentratedsulfuric acid with the mixture of oil and precipitated wax andcentrifuging the resultant mixture of waxy acid sludge and purifieddewaxed oil and thereby effecting their separation; the 'improvementwhich comprises, in the chilling operation, sub-cooling the oil belowthe temperature that would be required, if cold acid were added, tosubsequently produce purified dewaxed oil of the desired pour point,and, in the acid treating operation, adding the acid while at atemperature Within 10 F. of 150 F. to thereby speed the reaction andprevent freezing of the acid before the completion of the reaction.

' GEORGE J. STREZYNSKI.

